Brock could also be a main character. Since he has knowledge about Pokémon care and breeding, he could be Ash's colleague in the fanfiction. They could work together on projects related to Pokémon health and nutrition.
Another possible main character could be Misty. She could visit Ash at the university or research facility he is working at. And they could discuss new findings about water - type Pokémon, given Misty's specialty in that area.
A young girl named Mia might be a character too. She is also a Glacion fan and is very competitive. She challenges Ash to various Glacion - related challenges, like a Glacion knowledge quiz or a race to find a hidden Glacion item in the forest.
May could be one of the main characters. She could join Ash on his journey and share her knowledge about Hoenn's Pokemon with him. Another could be Brock, still tagging along to offer his expertise in Pokemon care.
Well, Pikachu could still be a main character. Even if Ash hates everyone, Pikachu might be the one trying to bring back the old Ash. Maybe Team Rocket could also be main characters. They are always around Ash, and his new - found hatred could make their interactions even more interesting. They might be confused by his change or even try to take advantage of it.
His best friend from before the war could be a main character. This friend might have been waiting for Ash's return and now has to deal with the changed Ash.
Mallow is another great choice. With her love for cooking and Pokémon, she could use her skills to create special Pokémon food for Ash's team. This could lead to some fun and heartwarming moments between them, and also bring the whole harem together as they enjoy the food.
It could be that there is a young, impressionable character who looked up to Ash Aura. After the betrayal, this character is confused and starts to question his own beliefs. There might also be a powerful mage in the story who has the ability to see the truth behind Ash Aura's actions and is trying to prevent the chaos that the betrayal has caused.
Pikachu would definitely still be there. It's Ash's most loyal companion, and it would be interesting to see how their relationship might change now that Ash is a girl. Maybe Pikachu would be more protective or show a different kind of affection.
Serna herself could be a main character. She might be Ash's love interest or a sister - like figure. Her reaction to Ash's return would be crucial in shaping the story. Maybe she is overjoyed at first but then realizes that Ash is not the same person who left for war.
One possible main character could be Misty. She could be a student at Harem High School who has a long - standing friendship with Ash. Her feisty and determined personality would add a lot of drama and interaction to the story. She might be jealous of the attention Ash gets from other students, creating some interesting relationship dynamics.
Pikachu, of course. It's always been Ash's closest partner.